The present invention relates to an apparatus and system for dispensing fluids and, more particularly, an apparatus and system for dispensing small volume fluid samples to microfluidic devices.
A recent development in analytical testing has been the miniaturization of testing equipment used to detect and analyze the constituents of samples of chemical and biological fluids. Using tools and techniques developed for producing electronic devices, intricate microfluidic systems can be inexpensively mass produced. Improved performance, reduced time, reduced reagent consumption, enhanced availability and ability to automate have provided impetus for the development of “microfluidic” or “micro-total analysis” devices and systems, also commonly referred to as a “lab-on-a-chip.”
Microfluidic devices are typically constructed by laminating multiple layers of glass, silicon, metal, polymer and other organic and inorganic materials. One of more of the layers includes microscale structures and voids such that when the layers are assembled microfluidic channels are formed for the flow and storage of fluid in the device. A microscale or microfluidic channel is generally a fluid passage which has at least one internal cross-sectional dimension that is less than 500 micrometers (μm) and, commonly, has at least one internal cross-sectional dimension less than 100 μm. Electrodes may be connected to one or more layers of the device to enable connecting an external power source, instrument or control to a transducer or other circuit formed on a layer of the device. Very small samples of liquids and gases, typically, a few nanoliters, introduced to or stored in the microfluidic device may be mixed, reacted or separated from a reagent for the purposes of performing a chemical or physical analysis of the fluid sample.
The movement and control of fluid flow in the channels of the microfluidic device may be accomplished by either forcing pressurized fluid into the device with an external pump or by pressurizing the fluid with a pump(s) built into the microfluidic device. The pressure differential to move fluid within the microfluidic device may be provided by a number of fluid drivers, such as a piezoelectric pump, micro-syringe pump or electroosmotic pump, that may be mounted internal or external to the device. However, a microfluidic device may also utilize a chemically induced pressure differential or inherent fluid force, such as gravity, hydrostatic pressure, capillary force, and absorption by a porous material, to produce fluid flow within the device. Microfluidic devices also commonly include active and passive valves to control the flow of fluid. Passive valves such as check valves are activated by the pressure and flow of the fluid. Active valves may be actuated pneumatically, electromechanically, mechanically or manually, to control fluid flow in the microfluidic channels of the device.
Miniscule samples of fluids, such as whole blood, bacterial cell suspensions, protein and antibody solutions, are introduced to the microfluidic device through one or more sample inlets and are mixed, separated and reacted with other substances introduced through other sample inlets or stored in the microfluidic device to determine a characteristic of the sample. Fluid is commonly introduced to the sample inlets of microfluidic devices through a micropipette. However, the small size of the microfluidic device makes manual pipetting of samples difficult and unreliable. On the other hand, automated sample dispensers are expensive and relatively inflexible because the dispensing mechanism must be programmed to position the fluid dispenser over the sample inlet of each type of microfluidic device or titer plate. In addition, pipetting is not suitable if the sample is to be injected under pressure because the sample inlet is not sealed. If the sample is to be introduced under pressure, the capillary tube used to deliver the sample is often cemented in the sample inlet well or into a ferrule which can be pressed into the sample inlet well of the device. What is desired, therefore, is a fluid dispensing system that can be accurately, freely and flexibly positioned to accurately dispense small samples of fluids to the sample inlet wells of a variety microfluidic devices.